Study On Steel Slag Used For In-situ Solidification Stabilization Of Ni/Pb Contaminated Soil

To develop a new way of high-value resource utilization of steel slag.Based on the application of solidification agent in heavy metal contaminated soil,the basic properties of three kinds of steel slag in Baosteel were investigated.The adsorption properties of different steel slag to Ni²⁺and Pb²⁺ions in heavy metal solution were studied.Finally,the converter steel slag powder was selected as the research object.The solidification effect of converter slag powder on the soil polluted by Ni²⁺and Pb²⁺heavy metals was studied.The effect of converter slag powder on the soil polluted by Ni²⁺and Pb²⁺heavy metals was investigated,the mechanism of curing Ni²⁺and Pb²⁺heavy metals by converter slag powder,the effect of the combination of converter slag powder and cement on the soil polluted by Ni²⁺and Pb²⁺heavy metals were studied,and a new kind of soil polluted by Ni²⁺and Pb²⁺heavy metals was developed.New materials of soil stabilizer polluted by heavy metals.The specific results are as follows:The basic properties of molten iron slag,converter slag,and EAF slag,such as leaching toxicity,mineral composition,grinding work index,activity index of gel sand,f-CaO content,and pore structure,were studied.The adsorption tests of different fineness steel slag in Ni²⁺and Pb²⁺solution were carried out,and the following conclusions were obtained:?1?molten iron slag has advantages in grinding work index and activity index of gel sand,but the f-CaO content was too high.It is easy to crack the solidified body due to the poor stability;the grinding work index and the activity index of cementitious sand of the electric furnace slag are not ideal.The grinding energy consumption is high,and the cementitious property is poor;and all aspects of the performance of the rotary furnace slag are suitable for use as the curing agent.?2?the fineness range of 320-340 mesh converter slag powder is the best for the adsorption of Ni²⁺and Pb²⁺ions in heavy metal solution.The solidification effect of converter steel slag powder on the soil polluted by Ni²⁺and Pb²⁺was studied.The influence of the amount of converter steel slag powder and solidification time on the solidification effect of Ni²⁺and Pb²⁺heavy metal polluted soil was tested and analyzed.In order to improve the solidification rate,the effect of phosphoric acid modified converter steel slag powder on the remediation effect of heavy metal polluted soil was studied.The analyzed effects were:?1?the addition of converter slag powder can significantly improve the pH value of heavy metal contaminated soil and create an alkali environment suitable for heavy metal passivation;?2?with the increase of converter slag powder,the leaching concentration of Ni²⁺and Pb²⁺in heavy metal soil decreased evidently,which had good remediation effect on heavy metal soil.With the increase of solidification time,the leaching concentration of Ni²⁺ion in heavy metal soil decreased significantly,while that of Pb⁺ion was relatively stable;?3?proper phosphoric acid treatment is conducive to the formation of better porous structure and increase of specific surface area and pore volume of phosphoric acid modified converter slag powder.Not only Ni²⁺and Pb²⁺ions are fixed on its surface by means of ion exchange,but also hydrous calcium silicate?C-S-H?is formed by hydration to exert the wrapping effect on heavy metal soil.When the amount of converter slag powder is 80g and the amount of phosphoric acid is 3.2ml,the converter slag powder modified by phosphoric acid had a good porous structure;when the amount of converter slag powder modified by phosphoric acid is 25%,it has a good remediation effect on heavy metal contaminated soil.In order to reveal the mechanism of solidification of Ni²⁺and Pb²⁺ions by converter slag powder,the solidification effect of converter slag powder on heavy metal contaminated soil at different solidification time nodes was studied by Fourier transform infrared spectrometer,and the solidification process of Pb²⁺and Ni²⁺ions and heavy metal in heavy metal contaminated soil by converter slag powder and the microstructure of the mixture of polluted soil and converter slag powder were revealed from the micro level.Furthermore,the above test and analysis results were confirmed by SEM and EDS.The observations were:?1?the steel slag powder of converter has a good curing effect on Pb²⁺and Ni²⁺ions in heavy metal polluted soil,the curing rate is over 90%in180d,and the least curing time is 3d.Pb²⁺and Ni²⁺ions are passivated in the form of PbCO₃,3Ni?OH?₂·2H₂O and Ni₂SiO₄respectively.?2?The solidification process of Pb²⁺and Ni²⁺ions in heavy metal contaminated soil can be divided into three stages:in the early stage?1-3 days?,the alkali environment in the mixture of heavy metal contaminated soil and converter steel slag powder is higher,which accelerates the formation of 3Ni?OH?₂·2H₂O,and the solidification mode is mainly ion exchange;in the middle stage?7-42 days?,the OH^-concentration in the mixture of heavy metal contaminated soil and converter steel slag powder decreases.The weakening of ion exchange and the enhancement of gel solidification promoted the formation of Ni₂SiO₄,and at the same time formed a large amount of CO₃^2-,which was beneficial to the formation of PbCO₃.In the later stage?56?180d?.A large amount of C-S-H gel was formed in the mixture of heavy metal contaminated soil converter steel slag powder,which encapsulated heavy metal contaminated soil and further enhanced gel solidification.?3?Curing Pb²⁺ions and Ni²⁺ions by ion exchange in high-alkalinity environment is stronger than that of calcium silicate hydrogel?C-S-H?.At the same time,the high alkalinity environment can inhibit the leaching of Pb²⁺ions and Ni²⁺ions in heavy metal contaminated soil,thereby further enhancing the solidification effect of converter slag powder on contaminated soil.Based on the Gaussian process regression,a soft sensing model was established to study the effectiveness of the model in predicting the curing effect of curing agent on Pb²⁺and Ni²⁺ions in polluted soil.It was found that the predicted results of the model were slightly smaller than the actual results,with an absolute error of-0.94?-0.62 and a relative error of-0.63%?-1.00%.In order to make up for the deficiency of unconfined compressive strength of heavy metal contaminated soil solidified by converter slag powder,the converter slag powder and ordinary portland cement were combined to prepare converter slag powder cement composite curing agent.The effects of the ratio of powder to binder,the amount of additive,the ratio of liquid to solid,and the curing time on the curing effect of the composite curing agent for Pb²⁺and Ni²⁺ions in polluted soil were studied by orthogonal test.The curing effect of the composite curing agent for Ni²⁺and Pb²⁺ions in polluted soil was verified by biochemical test.The curing effects of the composite curing agent on Ni²⁺and Pb²⁺ions in heavy metal contaminated soil were:?1?curing time and dosage are the main factors affecting the curing effect of composite curing agent on Ni²⁺and Pb²⁺ions;furthermore,the effect of powder binder ratio on the curing effect of different heavy metal ions is also obvious.?2?The composite curing agent has the best curing effect on Ni²⁺when the ratio of powder to binder is 3:7,the amount of additive is 25%,the ratio of liquid to solid is 1:3,and the curing time is 28 days.?3?When the ratio of powder to binder is 6:4,the amount of addition is 25%,the ratio of liquid to solid is 1:3,and the curing time is 28 days;the composite curing agent has the best curing effect on Pb²⁺.?4?The curing rate of composite curing agent for Ni²⁺ion can reach up to 96%?99%,while the curing rate for Pb²⁺ion is mostly below 96%.Therefore,the curing effect of composite curing agent for Ni²⁺ion is better than that of Pb²⁺ ion.